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The Biosphere

Chapter 58

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Biomes

• Biomes: a major type of ecosystem on land

• Each biome has a characteristic appearance

– Defined largely by sets of regional climatic conditions

• Biomes are named according to their vegetational structures

• Eight principle biomes

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Biomes

Predictors of biome distribution Temperature and precipitation

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Biomes• Tropical rain forests

– 140-450 cm rain/yr

– Richest ecosystems on land

– High temperature and high rainfall

– Very high diversity: 1200 species of butterflies in a single square mile

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• Savanna

– 50-120 cm rainfall/yr

– Tropical or subtropical grasslands

– Occur as a transition ecosystem between tropical rainforests and deserts

– Serengeti of East Africa

Biomes

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• Deserts

– 25-40cm rainfall/yr; unpredictable

• Plants and animals cannot depend on any rainfall

– 30˚N and S latitudes, rainshadows

– Vegetation sparse, animals adapted to little water availability

Biomes

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• Temperate grasslands: prairies

– Rich soils

– Grasses with roots that penetrate deep into the soil

– In North America converted to agricultural use

– Adapted to periodic fire

Biomes

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Biomes

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• Life depends on oxygen availability

– Oxygen per liter is only 5% of that in the atmosphere

• Oxygen added by photosynthesis and aeration from the atmosphere

• Oxygen is removed by animal and detritivores respiration, and through decaying organic matter

• Warm water holds less O2 than cooler water

Freshwater Habitats

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• Lake and pond habitats change with water depth– Intensity of light decreases with water

depth– Photic zone: area where light

penetrates and photosynthesis is possible

– Littoral zone: shallows at edge of lake– Aphotic (benthic) zone: below light

penetration level

Freshwater Habitats

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Lake Zones and Productivity

Freshwater Habitats

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Annual cycle of thermal stratification in a temperate-

zone lake

Freshwater Habitats

• Wind can force the layers to mix

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• Oligotrophic water: low in nutrients, usually high in oxygen

• Crystal clear conditions because of the low amount of organic matter

Freshwater Habitats

• Light penetrates deep in the water column

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• Eutrophic water: high in nutrients, densely populated with algae and plant material

• Low in dissolved oxygen in summer

Freshwater Habitats

• Light does not penetrate the water column

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Marine Habitats• 71% of the Earth’s surface is covered by

ocean• Continental shelves: near coastlines,

water is not especially deep– ~ 80km wide and 1m to 130m deep

• Average depth of the open ocean is 4,000 - 5,000m deep– Trenches: 11,000m deep

• Principle primary producers are phytoplankton (single cell or colonial)

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Marine Habitats

• Oceanic Zones

• Open oceans have low primary productivity

• Oligotrophic ocean: Low nutrient levels “biological deserts”

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Marine Habitats• Continental shelf ecosystems provide

abundant resources• Neritic waters: waters over the shelves

– High concentrations of nitrates and other nutrient

– Shallow, up welling occurs here• 99% of ocean food supply comes from

neritic waters• Petroleum comes almost exclusively from

shelves

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Marine Habitats

• Estuaries: shelf ecosystem where fresh water from streams or rivers mix with ocean water

– Intertidal habitat: area that is exposed to air at low tide but under water at high tide

– Salt marshes: in the intertidal zone

– Mangrove swamps: occur in tropical and subtropical intertidal zones

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Marine Habitats

Mangrove Swamp Louisiana Marsh

Coral Reef

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Marine Habitats• Banks and coral reefs

– Banks are local shallow areas on the shelves• Fishing grounds

– Coral reefs occur in subtropical and tropical latitudes

– Defining feature is stony corals• Algal symbioses: cnidarians and

dinoflagellates

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Marine Habitats

Upwelling regions: localized places where deep water is drawn consistently

to the surface

Green areas are upwelling regions

Dark blue are oligotrophic

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Marine Habitats• El Niño Southern Oscillation

– 2-7 years on an irregular and unpredictable basis

– Coastline waters become waters become profoundly warm

– Primary productivity unusually low– Weakening of the east-to-west Trade

Winds– Upwelling continues, but only recirculates

the thick warm surface layer

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Marine Habitats• El Niño can wreak havoc on ecosystems

– Plankton abundance can drop to 1/20th normal levels

– Fish stocks disappear– Seabirds and sea lion populations crash

• On land: – Heavy rains produce abundant seeds and

land birds flourish– Increase rodent population– Increase predator population

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Marine Habitats

El Niño winter

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Marine Habitats

• Deep sea: cold, dark place with fascinating communities

– Seasonless, 2-5˚C, pressure: 400-500 atms

• Food originates from photosynthesis in the sunlit waters

• 99% eaten as it drifts down through the water column

• Animals: small-bodied, thinly distributed

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Marine HabitatsHydrothermal vent communities: thick with life

• Large bodied animals• Do not depend on the

Sun’s energy for primary production

• Depend on sulfur-oxidizing bacteria

• Water temperature up to 350˚C

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Marine Habitats

• Once Trade Winds weaken a bit, the pressure difference that makes them blow is lessened, weakening the Trade Winds even more

– Shift the weather systems of the western Pacific Ocean 6,000km eastward

– Tropical rainstorms fall on Peru and Ecuador

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Human Impacts: Pollution

• Human impacts can cause adverse changes in ecosystems

• DDT: highly effective insecticide, sprayed in United States after WWII

• DDT is oil soluble and biomagnifies in the food chain

• Result of use:

– Populations of ospreys, bald eagles, and brown pelicans plummeted

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• Biomagnification of DDT concentrations in the food chain. Predatory bird species were affected because it made their eggshells so thin that the shells broke during incubation

Human Impacts: Pollution

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• Freshwater habitats are threatened by pollution and resource use

• Point source pollution: comes from an identifiable location

– Factories

– Sewage-treatment plants

• Laws and technologies can be applied because the source is known

Human Impacts: Pollution

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• Diffuse pollution: is exemplified by eutrophication caused by excessive run-off of nitrates and phosphates– Dissolved oxygen declines– Fish species change, carp take the

place of more desirable species• Can originate from thousands of lawns,

farms, golf clubs…• Solutions depend on public education and

political action

Human Impacts: Pollution

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• Pollution from coal burning: acid precipitation– When coal is burned sulfur oxide is

released– Sulfur oxide combines with water in the

atmosphere to create sulfuric acid• Mercury emitted in stack smoke is a

second potential problem– Mercury biomagnifies: causes brain

damage in humans

Human Impacts: Pollution

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• Acid precipitation and mercury pollution affect freshwater ecosystems

– pH levels below 5.0, many fish species and other aquatic animals die or are unable to reproduce

– Mercury accumulates in the tissues of food fish: dangerous to public health

Human Impacts: Pollution

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• Terrestrial ecosystems are threatened by deforestation

– Single greatest problem is deforestation by cutting or burning

Human Impacts: Pollution

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• Deforestation consequences

– Loss of habitat

– Major contributing factor in increased desertification

– Loss of nutrients from soils

– Eutrophication of lakes, streams, and rivers

– Disruption of the water cycle

– Loss of topsoil

Human Impacts: Pollution

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• Overfishing of the ocean

– Crisis proportions -- single greatest problem in the ocean realm

Poaching on terrestrial animals increases when fish populations decline

Human Impacts: Pollution

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• Aquaculture is only a quick fix

– Dietary protein needs of many aquacultured fish are met with wild-caught fish

– Often damage natural ocean ecosystems: clearing of mangrove swamps for aquaculture area

Human Impacts: Pollution

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• Pollution effects in the ocean

– Plastic found washed up on beaches in remote areas

– Waters are laced with toxic chemicals

– Biopsy of tissue from Arctic killer whales reveal high levels of pesticides and flame-retardant chemicals

Human Impacts: Pollution

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• Destruction of coastal ecosystems– Estuaries subjected to severe

eutrophication– Destruction of salt marshes

• Major contributing factor to hurricane destruction along the coast of Louisiana

• Had marshes been present, Katrina might not have caused so much damage

Human Impacts: Pollution

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• Stratospheric ozone depletion

– Ozone hole: over Antarctica between 1/2 to 1/3 of original ozone concentrations are present

Human Impacts: Pollution

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• Over United States– Ozone concentration has been reduced

by about 4%• Stratospheric ozone is important because it

absorbs UV radiation (UV-B)• UV-B damages tissue increases risks for

– Cataracts– Skin cancer: 1% drop in ozone leads to

a 6% increase in skin cancer

Human Impacts: Pollution

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• Ozone depletion and CFCs: Major cause of ozone depletion are chlorine and bromine containing compounds in the atmosphere

• Use of CFCs are being phased out in many countries

• CFC are chemically stable in the atmosphere for many years

• Ozone depletion will continue to occur until all of the CFCs are broken down

Human Impacts: Pollution

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• CO2 and other gases in the atmosphere maintain the Earth’s average temperature at 25˚C

• Human activities are now changing the composition of the atmosphere; increasing the CO2 and other gas levels

• Because of the increase, global temperatures are increasing, causing global warming

Global Warming

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Global Warming

2005 was the warmest year on record

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Global Warming• Based on the outputs of all four models

– Temperature in Europe is predicted to increase by 2˚C-4˚C by 2080

– Increases in temperature will be disruptive• Snow cover in the Swiss Alps: 300 m

higher than today• Parts of southern Europe will receive

20% less precipitation• Cause major economic upheavals

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Global Warming

Concentrations of CO2 since 1958

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Global Warming

• Cause of global warming?

– Greenhouse effect: which is good in that it keeps the Earth warm enough for life

– But increase in CO2 emissions through burning of fossil fuels will continue to increase temperatures on Earth

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Global Warming

• How CO2 affects temperature

– CO2 absorbs electromagnetic radiant energy

– Earth receives radiant energy from the Sun

– Earth also emits radiant energy

– The Earth’s temperature will be constant only if the rates of these two processes are equal

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Global Warming

• The atmosphere allows in short wave radiant energy from the Sun, but does not allow the long wave radiant energy from the Earth to escape

• This is the same principle as a Greenhouse

Short wave- in, long wave - cannot get out, increase in

temperature in the greenhouse

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Global Warming• Other greenhouse gases

– Methane: 20 xs the heat trapping properties of CO2, less concentration in the atmosphere, less long-lived

– Methane is produced globally in anaerobic soils and fermentation reactions of ruminant mammals

– Methane is locked up in permafrost• Sudden release will cause large

perturbation in global temperature

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Global Warming• Other greenhouse gases

– Nitrous oxide: agricultural use of fertilizers is the largest source

– Energy consumption– Industrial use

• Evidence confirms global warming– Ice free seasons 2.5 wks longer– Ice at the North Pole decreased– Glaciers decreasing in size

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Global Warming

Disappearing glaciers

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Global Warming• Global temperature change has affected

ecosystems in the past and is doing so now

– Shift in species geographic ranges

– Migratory birds arrive earlier at their summer breeding grounds

– Insects and amphibians breed earlier

– Wild fruit fly populations-changes in gene frequency

– “bleaching” of reef building corals

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Global Warming• Problems

– Rate of warming today is rapid

– Evolutionary adaptations for species survival may not have time to occur

– Natural areas no longer cover the whole landscape

– Species that shift to higher altitudes may have reached the peak of the mountain

– Species’ habitat disappears entirely

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• Possible effects on human species

– Rising sea levels: 200 million people would be affected by increased flooding

• Coastal cities and entire islands could be submerged

– Frequency or severity of extreme events will increase (hurricanes, El Niño)

Global Warming

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• Effects on agriculture

– Positive: more CO2 tends to increase growth of some crops

– Increase pollen production causing more severe allergies

– More droughts in some regions

– Decrease in crop production in tropical areas

Global Warming

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• Human health– Frequent flooding = loss of safe

drinking water• Cholera and other epidemics may

occur more often– Tropical diseases may invade

nontropical countries• Malaria• Dengue fever

Global Warming